1. Field of the Invention
This invention relates to a diagnostic device that has an insulating pattern scored into a conductive coating on the device to facilitate analytical measurements; more particularly, to monitor filling of the device.
2. Description of the Related Art
A variety of medical diagnostic procedures involve tests on biological fluids, such as blood, urine, or saliva, to determine an analyte concentration in the fluid. The procedures measure a variety of physical parameters—mechanical, optical, electrical, etc.,—of the biological fluid.
Among the analytes of greatest interest is glucose, and dry phase reagent strips incorporating enzyme-based compositions are used extensively in clinical laboratories, physicians' offices, hospitals, and homes to test samples of biological fluids for glucose concentration. In fact, reagent strips have become an everyday necessity for many of the nation's estimated 16 million people with diabetes. Since diabetes can cause dangerous anomalies in blood chemistry, it can contribute to vision loss, kidney failure, and other serious medical consequences. To minimize the risk of these consequences, most people with diabetes must test themselves periodically, then adjust their glucose concentration accordingly, for instance, through diet, exercise, and/or insulin injections. Some patients must test their blood glucose concentration as often as four times or more daily.
One type of glucose measurement system operates electrochemically, detecting the oxidation of blood glucose on a dry reagent strip. The reagent generally includes an enzyme, such as glucose oxidase or glucose dehydrogenase, and a redox mediator, such as ferrocene or ferricyanide. This type of measurement system is described in U.S. Pat. No. 4,224,125, issued on Sep. 23, 1980, to Nakamura et al.; and U.S. Pat. No. 4,545,382, issued on Oct. 8, 1985, to Higgins et al., incorporated herein by reference.
Hodges et al., WO 9718464 A1, published on May 22, 1997, discloses an electrochemical device for measuring blood glucose that includes two metallized polyethylene terephthalate (PET) layers sandwiching an adhesive-coated PET intermediate layer. The metallized layers constitute first and second electrodes, and a cutout in the adhesive-coated layer defines an electrochemical cell. The cell contains the reagent that reacts with the glucose in a blood sample. The device is elongated, and the sample is introduced at an inlet on one of the long sides.
Nakai et al., U.S. Pat. No. 5,266,179, issued on Nov. 30, 1993, discloses an electrochemical system for measuring blood glucose, in which the sample application time is determined by a resistance drop between a pair of electrodes to which a constant voltage was applied.
White et al., U.S. Pat. No. 5,366,609, issued on Nov. 22, 1994, describes the same principle of monitoring the resistance drop between the electrodes to determine the time at which blood was applied to a dry glucose reagent strip. In both patents, a constant voltage is applied between working and reference electrodes to track resistance changes that result from the introduction of a blood sample to a dry reagent strip.
Accurately determining an analyte concentration generally requires a sufficient supply of sample. Yoshioka et al., U.S. Pat. No. 5,264,103, issued on Nov. 23, 1993, discloses a biosensor for electrochemically measuring concentration of an analyte, such as glucose, in a biological fluid. An impedance change indicates that a sufficient supply of sample has been supplied to the sensor.
Littlejohn et al., U.S. Pat. No. 4,940,945, issued on Jul. 10, 1990, discloses a portable apparatus that can measure pH of a blood sample. The apparatus detects the presence of a sample in a cell by injecting a constant current between a fill electrode outside the sample chamber and one of two electrodes inside the chamber. When the impedance decreases by at least two orders of magnitude, the meter recognizes that sufficient sample has been provided and emits a beep. The fill electrode is then cut out of the circuit that includes the two electrodes inside the sample cell, and measurements are made potentiometrically.
Crismore et al., U.S. Pat. No. 5,997,817, issued on Dec. 7, 1999, discloses an electrochemical sensor strip that includes a window through which a user can determine visually whether enough sample has been applied to the strip.
None of the above references discloses a mechanism for monitoring the movement of a blood sample into (and through) an electrochemical cell.